The gapfill process is a very important stage of semiconductor manufacturing. The gapfill process is used to fill a high aspect ratio gap (or feature) with an insulating or conducting material. For example, shallow trench isolation, inter-metal dielectric layers, passivation layers, dummy gate, etc. As device geometries shrink (e.g., critical dimensions <20 nm) and thermal budgets are reduced, void-free filling of high aspect ratio spaces (e.g., AR>10:1) becomes increasingly difficult due to limitations of conventional deposition processes.
Most deposition methods deposit more material on the top region than on the bottom region of a structure. The process often forms a mushroom shape film profile. As a result, the top part of a high aspect ratio structure sometimes pinches off prematurely leaving seams/voids within the structure's lower portions. This problem more prevalent in small features.
One approach to gap fill is high-density plasma chemical vapor deposition (HDP CVD). HDP CVD is a directional (bottom-up) CVD process that is used for high aspect ratio gap-fill. The method deposits more material at the bottom of a high aspect ratio structure than on its sidewalls. It accomplishes this by directing charged dielectric precursor species downward, to the bottom of the gap. The directional aspect of the deposition process produces some high momentum charged species that sputter away bottom fill. The sputtered material tends to redeposit on the sidewalls. Limitations due to overhang formation become ever more severe as the width of the gap to be filled decreases and the aspect ratio increases.
Another approach to gapfill high AR features is by use of a flowable CVD process. A flowable CVD process usually requires complicated deposition-cure-treatment processing. Therefore, there is a need in the art for gapfill methods that can deposit films in high aspect ratio structures.